1. Field of the Invention
The present invention relates generally to generation of graphical images, and more specifically to conversion of a vector description driven display into a raster image output.
2. Description of the Prior Art
Graphical displays are becoming increasingly common for use with computer systems. Higher quality color displays can show many colors at the same time, with 8 or more bits per pixel color resolution not being uncommon.
Some display systems, such as graPHIGS, a product available from International Business Machines, generate images on a CRT display using information supplied in data structures defining the various elements displayed on the screen. Displays of this type are sometimes known as vector description displays. Other graphical displays use a raster image, which is a rectangular array of pixels with each pixel being separately addressable. Such displays use some predetermined number of bits for each pixel in the array to determine the display color for that pixel.
It is sometimes desirable to transfer images available as a vector description to a raster format for display on another device or for printing. Such a capability is provided with the graPHIGS product which can generate a graphical data display manager (GDDM) file from a selected screen image. The GDDM file can then be converted to bitmaps suitable for a raster display. One problem with such conversion is that the graPHIGS package can display up to 256 different colors on a screen (8 bit color resolution), while the GDDM compatible files will only support 16 colors (4 bit color resolution). Thus, much color information is lost when translating a graPHIGS display which utilizes the full palette of available colors.
It would be desirable to provide a system and method for generating a raster image which retains all of the colors of an original vector description image. It would be further desirable for such a technique to be relatively easy to implement and use.